In the accumulation conveyor field it has long been desired to have a unit which can handle large, heavy articles and small, light articles on the same unit.
In prior accumulation conveyors where the force required to discontinue the conveyor drive when an article was stopped on the unit and to start the drive when the stopped article again moved has been provided by a sensor operated either by the weight or the movement of an article or both.
This meant that small, light articles could not operate a clutch or the like of sufficiently heavy duty for the conveyance of heavy articles so that light and heavy articles could not be mixed unless some extraneous power source such as air or electricity was resorted to which required complicated mechanism and was expensive and required space and much maintenance. An example of such a unit is disclosed by U.S. Pat. No. 3,225,893.
Efforts have been made to produce accumulation conveyors in which the power required to operate the clutches to discontinue and then continue the movement of the articles is provided by the conveyor drive which moves the articles conveyed, but such equipment to date has been so complicated as to be prohibitively expensive, undependable or require extensive adjustment or maintenance or all of these undesirable factors.
Examples of such units are disclosed by U.S. Pat. Nos. 3,219,172; 3,285,391; 3,156,345; 3,116,823; 3,164,246; 3,206,008; 3,136,406; and 3,232,415.